Heretofore, thinking in the fire protection art has been directed towards the use of multiple sprinklers for the protection of interior areas more than about one to two hundred square feet so as to limit the maximum average area protected by each sprinkler. As the perceived fire threat rises, the recommended protected area of coverage for each sprinkler is reduced. Such thinking has been embodied, for example, in accepted industry standards such as the Standard for the Installation of Sprinkler Systems, NFPA-13, issued by the National Fire Protection Association.
According to the National Fire Protection Association, NFPA-13 was first printed in 1896 under the direction of the Committee on Automatic Sprinklers and has been continuously revised since that time. NFPA-13 defines various requirements for sprinkler systems utilized in occupied interior spaces or "occupancies" with different fire hazard potentials. The NFPA-13 recognizes three general hazard categories for sprinkler systems: light, ordinary and extra. As defined by the NFPA-13, light hazard occupancies are those where the quantity and/or combustibility of contents is low and fires with relatively low rates of heat release are expected. Ordinary hazard covers those occupancies where the quantity and/or combustibility of the contents is equal to or greater than that of light hazard, ranging from low to high, where the quantities of combustibles is moderate and stock piles do not exceed twelve feet, such that fires with moderate to high rates of heat release are expected. Extra hazard occupancies are those where quantity and combustibility of the contents is very high and flammable or combustible liquids, dust, lint or other materials are present, such that the probability of rapidly developing fires with high rates of heat release is very high. The present invention is directed specifically to the protection of light and ordinary hazard occupancies, which define the bulk of most potential commercial installations.
NFPA-13 also specifies maximum areas of protection per sprinkler for the various hazards. For example, the normal maximum protection area limit per sprinkler for a sprinkler system in a light hazard occupancy is two hundred twenty-five square feet. The maximum protected area per sprinkler in an ordinary hazard occupancy is one hundred thirty square feet.
The protection area of a sprinkler is also defined by NFPA-13. The protection area of a sprinkler is at least rectangular and may be square, and equals "S".times."L". "S" is defined as the greater of the distance from the sprinkler in question to the farthest spaced, immediately adjoining sprinkler, upstream or downstream, on the same supply line, or twice the distance from the sprinkler in question to a wall where the sprinkler in question is the last sprinkler on a supply line extending in a direction towards the wall. "L" is the greater of the perpendicular distance to the farthest spaced branch line immediately adjoining either lateral side of the branch line supporting the sprinkler in question, or twice the perpendicular distance to the farthest spaced wall immediately adjoining either side of the branch line which supports the sprinkler in question and which lacks an immediately adjoining branch line between it and the wall. In the case of small rooms where there is overlapping sprinkler coverage, the protection area of each sprinkler is considered to be the area of the room divided by the number of sprinklers.
NFPA-13 specifies maximum spacings of fifteen feet between lateral, side-by-side immediately adjoining branch lines and fifteen feet between immediately adjoining sprinklers along the same branch line, and up to one-half those spacings for an immediately adjoining wall, for light hazard occupancies, for a permitted maximum total protection area per sprinkler of two-hundred and twenty-five square feet. NFPA-13 further specifies a maximum spacing of up to fifteen feet between lateral, side-by-side immediately adjoining branch lines or up to fifteen feet between immediately adjoining sprinklers on the same branch line and up to one-half those spacings in the case of an adjoining wall, for a permitted maximum total protection area per sprinkler of up to one-hundred and thirty square feet.
In 1973, Section 4-1.1.1.3 was adopted and incorporated into the NFPA-13 . That section stated:
Special sprinklers may be installed with larger protection areas or distance between sprinklers than are specified in Sections 4-2 and 4-5 when installed in accordance with the approvals or listing of a testing laboratory. PA1 Special Sprinklers-Installation of special sprinklers with protection areas, locations and distances between sprinklers differing from those specified . . . shall be permitted when found suitable for such use based on fire tests related to hazard category, tests to evaluate distribution, wetting of floors and walls, and interference to distribution by structural elements and tests to characterize response to sensitivity.
At the time, Sections 4-2 and 4-5 defined the maximum spacings and protection areas indicated above.
In 1987 that section of the NFPA-13 was amended to read:
Underwriters Laboratories, Inc. ("UL") is the independent laboratory most widely utilized in the United States for testing and listing sprinklers. Its main sprinkler test standard for sprinklers conforming to NFPA-13 is UL 199 for Automatic Sprinklers For Fire-Protection Service. At the time the present invention was made, UL 199 set forth test requirements for automatic sprinklers varying in nominal orifice size from 1/4 inch to 17/32 inch. The most widely sold and utilized ceiling sprinklers in the United States were and are nominally 1/2 inch in orifice size and are referred to as "standard orifice" sprinklers by UL, NFPA and the industry. Sprinklers of about 17/32 inch diameter were and are referred to as "large orifice" sprinklers.
Prior to the present invention, increased area coverage protection under NFPA-13 Section 4-1.1.1.3 had been offered only for light hazard occupancies by the modification of existing, standard orifice sprinklers. For example, in 1987, Central Sprinkler Corporation ("Central") introduced extended-coverage, with an adjustable pendent, standard orifice sprinkler, the EC-20, which was UL listed for light hazard occupancies with protection area coverages of up to four hundred square feet per sprinkler and up to 20 foot spacings between sprinklers and between branch lines with such sprinklers. After Central pioneered extended coverage in light hazard with a standard orifice ceiling sprinkler, others in the industry followed.
While Central demonstrated the possibility of providing extended coverage protection for light hazard with standard orifice sprinklers, several problems faced Central and anyone else seeking to provide ordinary hazard protection for extended coverage areas greater than the maximum one-hundred and thirty square feet protection areas specified in NFPA-13 for ordinary hazard listed sprinklers.
A first problem was that increasing the size of the protection area of a sprinkler requires exponentially greater quantities of water to be delivered by the sprinkler, necessitating higher operating pressures. For example, NFPA specifies and UL lists sprinklers for light hazard protection for various protection areas on the basis of a minimum average delivered density of 0.10 gallons per minute (GPM)/foot square (ft.sup.2) into the protection area. Listings for ordinary hazard protection required deliveries in the range of from 0.16 to 0.21 GPM/ft.sup.2. Recently this range has been reduced to one of 0.15 to 0.20 GPM/ft.sup.2.
The discharge coefficient or "K factor" of a sprinkler determines the amount of water delivered through the sprinkler as a function of water pressure at the sprinkler. The discharge coefficient equals the flow of water in gallons per minute through the orifice of the sprinkler divided by the square root of the pressure of the water fed into the sprinkler in pounds per square inch. UL 199 defines a standard orifice sprinkler (1/2 inch diameter) as one having a discharge coefficient of 5.3 to 5.8.+-.5 percent. It also defines the discharge coefficient of a large orifice sprinkler as ranging between 7.4 to 8.2.+-.5 percent.
A standard orifice sprinkler requires a minimum pressure of about 16 psi in order to provide a minimum density of 0.10 GPM/ft.sup.2 over a conventional two-hundred and twenty-five foot protection area (spacings of fifteen feet between sprinklers and fifteen feet between branch lines). Increasing the spacings by one-third to twenty feet nearly doubles the area of average coverage per sprinkler (up to four hundred square feet), but requires a minimum pressure of about 50 psi, more than three hundred percent greater than the minimum pressure required for fifteen-foot spacings.
To provide the minimum ordinary hazard densities of 0.15 GPM/ft.sup.2 over the standard 130 square foot protection area with a standard orifice sprinkler requires a minimum pressure of about 12 psi. To extend the coverage to a 225 square foot area (15 foot maximum spacings) requires a minimum pressure of about 36 psi for such sprinklers. Increasing the spacings of standard orifice sprinklers to sixteen feet square, eighteen feet square and twenty feet square would require minimum sprinkler head pressures of nearly 50 psi, about 75 psi and over 100 psi, respectively. To provide 0.20 GPM/ft.sup.2 to the same fifteen, eighteen and twenty foot square areas would require minimum pressures of about 65, 85, 135 and over 200 psi with standard orifice sprinklers.
It is believed that a minimum pressure requirement of about 35 psi per sprinkler would necessitate the provision of a booster pump in at least some of the potential ordinary hazard occupancies in the United States, that a minimum requirement of about 50 psi would necessitate a booster pump in a majority of such occupancies, that a minimum requirement of 60 psi would necessitate a pump in eighty to ninety percent of such occupancies, and that a minimum requirement of about 75 psi would necessitate a pump in virtually all potential ordinary hazard occupancies. The cost of providing such a pump typically ranges upwards from about $35,000. Thus, many, if not most, potential ordinary hazard occupancies would require a booster pump to support extended coverage, standard orifice sprinkler systems.
A second problem was that no one knew if the quantities of water needed to be delivered could be successfully delivered with an acceptable level of uniformity over such extended areas or specifically how to do so. Merely increasing pressure to a conventional, light or ordinary hazard sprinkler or even to a conventional extended coverage light hazard sprinkler, does not predictably provide extended coverage distribution or deliver higher densities of water to a protected area. Virtually all existing ordinary hazard sprinklers have deflectors which severely limit their water discharge pattern and thus the protection area of the sprinkler. Increasing pressure will simply cause the sprinkler to deliver more water over the same limited area. As was just discussed, the delivery of water densities required for the upper end of ordinary hazard protection through an existing, standard orifice, extended coverage sprinkler over an area of sixteen or more feet square necessitates a booster pump in many if not most occupancies.
Even where pressure is boosted, adequate water distribution is not assured. At high pressures, distributed water may mist before reaching the protection area, and thus not be delivered. Another possibility is that the distribution pattern may collapse as the sprinkler deflector is effectively overwhelmed by the water column and a more restricted distribution pattern actually developed at higher pressures.
A third problem was that neither UL nor any other recognized testing laboratory had an established procedure or set of standards to test sprinklers or sprinkler systems for extended coverage listings in ordinary hazard occupancies. Although the possibility of providing such sprinklers had existed since at least 1973 under NFPA-13, no one ever tested or even proposed to test such a sprinkler.
Sprinkler engineers typically design sprinklers to satisfy recognized performance tests and standards, such as those of UL. Lacking recognized and established tests or performance standards, ordinary sprinkler engineers had no clear understanding of what to design to provide extended coverage, ordinary hazard protection.
As a practical matter, a sprinkler without a UL listing or a listing or approval by another of the recognized, major independent testing laboratories or associations in the United States would have little, if any, commercial value due to the requirements of various state and local governments and various fire insurers.